1. Field of the Invention
The present invention relates to cassettes for the storage and sterilization of dental and surgical instruments.
2. Description of the Prior Art
Dental instrument sterilization cassettes are devices which hold contaminated dental instruments during a sterilization process. Contaminated instruments are stored within a sterilization cassette, which is then placed in a sterilizer and subjected to a flow of sterilizing vapor. Sterilization cassettes are usually provided with a series of slots or holes to allow the flow of sterilizing vapor to pass through the cassette and over the instruments.
In today's dental practice, an ever-increasing volume of contaminated dental instruments requires effective sterilization. Given the rapidly increasing cost of dental services, and the heightened competition within the dental profession, the need for cost effective instrument sterilization is clear. In improving instrument sterilization efficiency, some important factors include: improved instrument storage capacity, convenient cassette retention of a range of instrument sizes, cassette capacity to serve the sterilized instruments to dental personnel in an operating theatre, and thinner cassette profiles (to increase cassette stacking efficiency within an autoclave).
Another factor, the advent of the AIDS epidemic, has focussed attention on instrument sterilization in another way. In particular, the danger inherent in AIDS-contaminated blood has created a demand for instrument sterilization cassettes which pose the lowest risk of accidentally exposing health care workers to contaminated instruments. Dependable instrument retention and cassette latching mechanisms are the principal factors in addressing this need.
As regards instrument sterilization efficiency, instrument storage capacity is a primary consideration. For example, the device shown in U.S. Pat. No. 5,084,251 of Thomas stores instruments in only one half of the sterilization cassette, yielding a relatively low instrument storage capacity. On the other hand, U.S. Pat. No. 4,959,199 of Brewer shows a sterilization cassette with instruments stored in both cassette halves, with an attendant increase in instrument storage capacity.
These instrument sterilization cassettes also reveal the usual deficiencies in approaches to instrument retention. In the opened Thomas cassette, the instruments always rest loosely on the supports, resulting in a vulnerability to spillage. When the Thomas cassette is closed, the instruments are secured in the supports by retaining bars attached to the upper half of the cassette.
Alternatively, the Brewer cassette has instruments stored on both halves in removable trays with "snap-in" supports. These supports only accept instruments sized to fit into the non-adjustable "snap-in" retainers. Thus, if different sized instruments are to be stored, Brewer requires a replacement tray fitted with appropriately sized "snap-ins." The "snap-in" supports are capable of insecure, loose acceptance of instruments smaller than the "snap-in" size, thereby creating a risk of instrument spillage.
Furthermore, these instrument storage and retention schemes also may detract from the application of these cassettes as instrument servers. In this role, an opened instrument sterilization cassette, situated on a working surface in an operating theatre, presents the instruments for removal as needed by a dental assistant or dentist. For this application, the Thomas cassette is spacially inefficient in only providing storage on one half of the cassette. The Brewer cassette is not optimal because of the concentration required to pull the stored instruments out of the "snap-in" retainers.
Turning to the need to reduce the exposure of health personnel to contaminated instruments, the dependability of cassette latching mechanisms becomes paramount. For instance, since the tops and bottoms of the Brewer and Thomas cassettes are not structurally obvious, these cassettes could be prone to upside-down opening. In this event, the loose instruments in the opened Thomas cassette could spill.
Brewer, on the other hand, shows intermediate locking plates providing additional security against spillage in the case of accidental opening. However, since these plates are not required to secure the instruments within the "snap-in" retainers, they may be forgotten by a health worker. Thus, any inappropriately small instruments stored in the Brewer "snap-ins" could be vulnerable to this type of spillage.
In addition, the toughness and durability of cassette latching mechanisms are key in avoiding accidental openings. These references' latch mechanisms are situated on the cassette exteriors, and are thus subject to abuse and possible accidental opening. Brewer's latch is particularly susceptible to inadvertent opening since a mere depression of an exposed hinge tongue causes the latch to release.
Finally, the references also show perforated cassette bodies which do not optimally drain away instrument debris during the sterilization operation. The referenced cassettes show numerous corner surfaces where debris from the sterilized instruments could catch and collect. Such debris retention is undesirable in any sterilization vessel.
Additional dental instrument sterilization cassettes are shown in U.S. Pat. No. 4,541,992 of Jerge et al., and U.S. Pat. No. 4,854,475 of Riihimaki.